Process of tawing skins.



NITED STATES I PATENT .rrrcn.

GEORGE IV. ADLER, OF PHILADELPHIA, PENNSYLVANIA.

I PROCESS OF TAWING SKINS.

SZPECIFIOATION forming n of Letters Patent Ne. 638,685, dated. December12, 1899. Application filed August 17, 1897. Serial No. 648,565. (Nospecimens) To all whom, it may concern:

Be it known that I, GEORGE W. ADLER, a citizen of the United States,residing in the city of Philadelphia, State of Pennsylvania, haveinvented certain new and useful Improvements in Processes of TawingSkins with Aluminium Compounds, of which the following is a full, clear,and exact specification.

My invention relates to the insoluble tawing by means of aluminium saltsand chromic oxids of hides and skins that have been prepared for tanningby any usual beam-house treatment; and it consists of the process andcomposition hereinafter described, whereby the oxids or basic salts ofaluminium and of chromium are separated out of their compounds in thepresence of the skin and insolubly combined successively with the tissues of the skin resulting in the production of an insolubly-tawed skinwhich partakes of the nature of both alum-tawed leather and chrome-tawedleather in that it possesses the appearance, touch, fine grain, andsoftness characteristic of and peculiar to the former,while it has alsothe perfectly insoluble nature which distinguishes the latter.

The essential features of my process consist in a preliminary treatmentof the skin, composed of three consecutive steps or actsviz., first,tawing the skin-tissues with an aqueous solution of aluminium sulfateand sulfate or chlorid of sodium, preferably the chlorid, then givingfixation to the same by means of an aqueous solution of hyposulfite ofsoda, as heretofore practiced in the art, and finally reapplying to theskin thus treated a solution in lesser quantity than at first of theingredients first applied-viz., aluminium sulfate and asodium salt. Athoroughly-tawed skin is thereby produced which is insoluble in coldwater or even in very warm water and which will make merchantableleather of superior quality, fine grain, and full and plump body, thelast-named quality being the result of the second subjection of the skinto the alum and sodium-salt bath, thereby overcoming an insuperableobjection heretofore existingviz., the thinning of the skin by theaction of the sodium hyposulfite after the first alum treatment. If asuperior quality of alum leather is desired, the skins taken from thisfinal bath of aluminium sulfate and sodium salts are Well adapted to befinished by the methods usually employed in finishing chrome-leather.If, however, it is desired to treat the tawed skin in the chromiccompound, hereinafter described,to render it thoroughly insoluble inboiling water before subjecting it to any usual finishing method, mypresent invention comprises, as a final and fourth step in the process,the subjection of such alu m-tawed skin to a bath of chrome-alum, inconjunction with sodium sulfate and potassium or sodium acetate, withoutthe aid of any free acid, whereby the chromealum is decomposed whenbrought into the presence of the skin and the oxid of chromium isseparated out in the presence of and insolubly combined with thepreviously-sawed hidetissues, a result which has never before beenaccomplished with chrome-alum or previously-reduced chromic salts.

In the practice of my invention I use a drum as a preferable mechanicalmeans of carrying out my process, as the tanning solution requires lesswater in such a device and is thereby more economically employed.

For every one hundred pounds of skins prepared for tanning I prepare asolution in two gallons of water of three pounds of aluminium sulfateand six pounds of fine common salt. This liquor is put in the drum withthe skins and run for about half an hour. I then prepare asecondsolution by dissolving about ten pounds of hyposulfite of soda in aboutthree gallons of warm water and add this solution to the liquor andskins still in the drum and run the drum for about fifteen or twentyminutes. I then prepare a third solution by dissolving about two poundsmore of aluminium sulfate and three pounds more of fine common salt, andthis solution is also added to the liquor and skins in the drum. Theskins are now run in this liquor for a half hour or more, or longer, ifneed be, until the skins show by inspection that they have acquired therequisite plumpness. The skins are then taken from the drum and arepreferably rinsed off by a single dipping of them separately in cleanwater and are then horsed up for several hours to drain.

The quantities of materials used as above specified may be variedslightly in the three several steps, while retaining the proportionssubstantially as stated. For economy of operation I have described thethree several solutions as being exhibited to the skins in the same drumin a certain order at intervals; but the same results are obtained ifthe skins are submitted to the three solutions separately butconsecutively and in the order described.

The old liquor being drawn ofi": from the drum, the skins (if notpreviously dipped in water when taken from the last alum-bath) are to berinsed in clean water to remove any free acid or excess of tawingmaterials adhering to the skin from the previous bath. They are thenagain put back into the drum, into which my initially chemically neutralchrome liquor, hereinafter described, is to be introduced and withoutwater or free acid of any kind. For this bath I employ not less thanthree nor more than six gallons of such chrome liquor to each onehundred pounds of skins. The chrome liquor is compounded as follows: Idissolve in five gallons of water from five to six pounds ofchrome-alum, two and one-half to three pounds of sodium sulfate, two andone-half to three pounds of sodium chlorid, and twelve ounces to onepound of potassium or sodium acetate or its equivalent. The skins arerun in the drum in this liquor for about an hour or until they havetaken up all or nearly all the liquor and show thorough penetration ofthe chromic compound. At this stage they will be found to be perfectlyinsoluble in boiling water. They can then be removed from the drum andwashed and finished, as usual in kid-leather dressing.

For heavy skins the neutral chrome liquor may be increased to six oreven seven gallons to each one hundred pounds of skins. As the activesodium salt in this solution is the sulfate, the chloride being usedonly to prevent tightening of the skin fibers, the chlorid may beomitted if the sulfate of sodium is increased by an amount equal toone-half the weight of the chlorid as given in the above formula. It mayalso be observed that the quantities of each ingredient named may bevaried slightly, provided the proportions stated be substantiallyretained.

Heretofore it has been proposed in the patents granted to Schultz, bothdated January 8, 1884:, to deposit the chromic oxid on the hide-tissues,insolubly combining the same therewith by presenting the chromiccompound to the skin as chromic acid or as a bichromate in the presenceof inorganic acid, and after impregnating the skin therewith to separateout the oxid by a chemical reduction of the acid by means of asulfurous-acidproducing salt, such as hyposulfite of soda, in thepresence of a decomposing acid; but this method requires as distinctivesteps or features that the chromic salt when presented shall be anacidified or acid solution and not already reduced to an oxid, thatthere shall necessarily be two separate, distinct, and sequential bathsor presentations, that there shall be a free inorganic acid in one orboth of the baths producing sulfurous acid from the sulfite and in thepresence of the chromic acid to be acted upon and in quantity capable ofchemically reducing the same and converting it into an oxid, and thatthis reaction shall take place on and in the presence of the hide to betreated.

The distinctive features of my process (which is radically different inevery respect from the foregoing) are primarily that no free acids,either organic or inorganic, are employed, that the skin is firstalum-tawed, and finally that it is treated with chromic oxid presentedas an alreadyreduced salt, the oxid being separated out of the compoundnot by a chemical reduction, but separated out and insol ubly combinedwith the previously-tawed hide-tissues by what is apparently a processof dialysis, this result being effected by combining with the chromealum the requisite inorganic salts of sodium and the requisite alkalisalt of an inorganic acid in suitable proportions, as stated.

The chemical reactions which take place are not well understood norsatisfactorily explainable in the light of present chemical knowledge,and this is due mainly to the fact that the presence of the organicmatters of the skin to be acted on radically change the chemicalequations.

It has long been known that chrome-alum and sodium sulfate perform atawing function-41 6., convert raw skin into leather; but the resultantproduct is open to various objections, principally the instability ofthe compound of chromium salts with the hide fiber, it being easilysoluble even in cold water. When, however, a soluble organic acidcompound is added to said elements in proper relative proportions and askin is exhibited thereto, undoubtedly a new chemical reactionsupervenes, (probably a separating out of chromic oxid and itsprecipitation in nascent condition in the hide fiber,) and the resultantcompound is an insoluble one and capable of resisting the test withboiling water. That the skin itself acts in or is the initial cause ofthis reaction seems certain, as it will not take place in its absence.Why the organic acid compound produces the separating out and depositionof nascent chromic oxid when the skin is brought into the presence gflasolution of the three elements I am unable to explain, even after acareful search in published technical works and inquiry of leadingchemists; but I do know, however, that free acid in the solution, eitherorganic or inorganic, added as an element-4;. 6., other than as producedby the decomposition of the chemicals employed in the presence of theskins-will retard, if not prevent, the reaction described, and I havefound after repeated trials that an alkali salt of an organic acid, suchas acetate of potassium or sodium, is the most available to produce thedesired result. While, however, I have specified sodium or potassiumacetate as the particular salt of an organic acid which is to be used, Idesire it to be understood that the corresponding salts of neighboringorganic acids in the series, which are well understood to have in manyrespects similar properties, may be employed.

The hyposulfite of soda used in the described process is the saltcommonly sold under that name, sometimes called by chemists thiosulfateof soda and answering to the formula Na S O The sulfate of aluminaemployedis that commonly sold under that name and sometimes asconcentrated alum, and it is usually united with sulfate of potash whensold as common alum; but in the latter case to carry out my process adouble quantity thereof must be used. The chrome-alum employed is thecommonly-sold lump chrom ealum of commerce and is usually a doublesulfate of chromium and potassium.

Having thus described my invention, what I claim as new, and desire tosecure by Letters Patent, is-

1. In the art of alum-tawing, the process which consists in firstsubjecting skins prepared for tanning to the action of a solution ofaluminium sulfate and of inorganic salts of sodium, then furthertreating such skins in an aqueous solution of hyposulfite of sodium, andfinally adding to the bath a second solution of the ingredients firstused but in a slightly-less quantity, the skins being successively actedupon by the bath in its several conditions substantially as described.

tion of chrome-alum, sodium sulfate, sodium chlorid and potassium orsodium acetate, admixed in the proper proportion,substantially asspecified.

4. In the art of tawing hides and skins pre* pared for tanning,theprocess described which consists first, in submitting them to thesuccessive action of dissolved aluminium sulfate and an inorganic sodiumsalt, then to an aqueous solution of hyposulfite of sodium, then to therepeated action of aluminium sulfate and an inorganic sodium salt andfinally drawing off the old liquor from the apparatus and subjecting theskins to the action of an aqueous solution of chrome-alum, inorganicsodium salts and a potassium or sodium salt of acetic or a neighboringorganic acid of that series, substantially as described.

In testimony whereof I have hereunto affiXed my signature this 29th dayof March, A. D. 1897.

GEORGE W. ADLER.

\Vitnesses:

Gno. W. REED, H. T. FENTON.

